Hard to be certain without context. This appears to be for deserialization? I think it has a happy path that could work as expected.
For example:
int main()
{
int x = 42;
char buffer[sizeof(x)];
memcpy(buffer, &x, sizeof(int));
int index = 0;
int result = read_int_from_stream(sizeof(int), index, buffer);
printf("Result: %d\n", result);
}
That said, there are a few things you could change about the code.
A likely issue is if the caller passes a value of "count" that is not equal to "sizeof(int)". If "count" is bigger, then you have undefined behaviour (likely manifesting as overwriting adjacent memory to "dst"). If "count" is smaller, then you have undefined behaviour as some part of "dst" remains uninitialised, likely manifesting as unexpected return values. It would be simpler to remove the parameter and use sizeof(int) rather than accept a parameter that could be potentially incorrect.
Other possible issues include:
Caller passes a negative "count"
Caller passes an invalid "src" buffer pointer (e.g. uninitialised, null)
Buffer pointer is valid but points to uninitialised data
Buffer data was never generated from the bit pattern of an int
Buffer data comes from another system with different endianess or sizeof(int)
"index" is or becomes out of range with respect to the buffer length
Also, it would be nice if "src" were const.